Particle beam irradiation apparatus, treatment planning unit, and particle beam irradiation method

ABSTRACT

A particle beam irradiation apparatus includes a synchrotron, two scanning electromagnets, an beam delivery apparatus for outputting an ion beam extracted from the synchrotron, and an accelerator and transport system controller, and a scanning controller. These controllers stop the output of the ion beam from the beam delivery apparatus; in a state where the output of the ion beam is stopped, change the irradiation position of the ion beam by controlling the scanning electromagnets; and after this change, control the scanning electromagnets to start the output of the ion beam from the beam delivery apparatus and to perform irradiations of the ion beam to at least one irradiation position a plurality of times based on treatment planning information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a particle beam treatment system, andmore particularly to a particle beam irradiation apparatus for treatingan affected part by irradiating it with charged particle beamscomprising proton ions, carbon ions, or the like, and a treatmentplanning unit using this particle beam irradiation apparatus, and aparticle beam irradiation method.

2. Description of the Related Art

A treatment method for treating a patient with cancer or the like byirradiating the affected part of the patient with charged particle beamssuch as proton beams is known. The treatment system used for thistreatment includes a charged particle beam generating unit, beamtransport system, and treatment room. The charged particle beamaccelerated by the accelerator of the charged particle beam generatingunit reaches the beam delivery apparatus beam delivery apparatus in thetreatment room through the beam transport system, and after beingscanned by scanning electromagnets provided in the beam deliveryapparatus beam delivery apparatus, the charged particle beam is appliedfrom a nozzle to the affected part of the patient. A treatment methodusing such a treatment system is known that includes the steps of:stopping the output of the charged particle beam from the beam deliveryapparatus; and in a state where the output of the charged particle beamis stopped, controlling the scanning electromagnets to change theirradiation position (spot) of the charged particle beam (so-called“scanning”) and to start the output of the charged particle beam fromthe beam delivery apparatus after the aforementioned change (see, forexample, European Patent Application No. 0779081A2 [FIG. 1 and thelike]).

In the above-described conventional particle beam treatment system, inorder to reduce to a minimum the exposure of normal tissue to radiationand perform a proper treatment with neither too much nor too littleirradiation, the beam delivery apparatus has an irradiation dose monitorand/or beam position monitor for estimating the irradiation dosedistribution, located at the downstream side of the electromagnets andimmediately in front of a patient to be irradiated. In many cases, thismonitor is of a type that accumulates charges ionized by the passage ofbeams in a capacitor, and that reads the voltage induced by thecapacitor after spot irradiation. The capacity of this capacitor isdetermined so as to permit the amount of ionized charges by the spotsubjected to a largest irradiation dose.

For the above-described capacitor, as the capacity decreases, the outputvoltage increases, thereby enhancing the resolution. Conversely, as thecapacitor increases, the resolution decreases. Such being the situation,if the difference in irradiation dose between the spot subjected to thelargest irradiation dose and that subjected to the smallest irradiationdose can be reduced, the capacity of the capacitor could becorrespondingly reduced to enhance the resolution. This would effect thepossibility of detecting more correctly an actual irradiation dose.However, the aforesaid conventional art does not particularly giveconsideration to the above-described reduction of the difference inirradiation dose, thus leaving room for improvement in the detectionaccuracy with respect to the actual irradiation dose.

Meanwhile, when performing irradiation to each spot, a targetirradiation dose is set on a spot-by-spot basis. Once an integratedvalue of irradiation dose detected by the irradiation dose monitor hasreached the target value, a beam stop command is outputted to theaccelerator, and in response to it, the accelerator stops the output ofa charged particle beam. With typical accelerator such as a slow cyclingsynchrotron or a cyclotron, even if the beam stop command is inputted asdescribed above, strictly speaking, it is not impossible that someamount of response delay occurs rather than the output of the chargedparticle beam immediately stops. In such a case, even after theaforementioned target value was reached, the charged particle beamcontinues to be applied to the pertinent spot for the time period duringthe response delay time. This leaves room for improvement in the controlaccuracy with respect to the irradiation dose of the charged particlebeam.

Since the irradiation dose monitor is an machine, it is difficult toperfectly eliminate the possibility that the irradiation dose monitorcauses a malfunction or failure. Also, since the target irradiation dosefor each spot is usually a value transmitted from a data base or a valuecalculated based on the transmitted value, it is not impossible that animproper value is inputted at the stage of the transmission or thecalculation. However, the above-described conventional art does notparticularly give consideration to such a monitor abnormality or aninput error. This leaves room for improvement in the prevention ofexcessive irradiation of charged particle beams due to theaforementioned monitor abnormality or input error.

Furthermore, when performing irradiation to each spot, a targetirradiation dose is set on a spot-by-spot basis. Once the integratedvalue of irradiation dose by the irradiation dose monitor has reachedthe target value, a beam stop command is outputted to the accelerator,and in response to it, the accelerator stops the output of the chargedparticle beam. Regarding such a beam stopping function, it is notimpossible that equipment associated with this function causes amalfunction or failure, as well. However, the above-describedconventional art does not particularly take a malfunction of such a beamstopping function into consideration. This leaves room for improvementin the prevention of excessive irradiation of charged particle beams dueto the above-described malfunction or failure of the beam stoppingfunction.

Accordingly, it is a first object of the present invention to provide aparticle beam irradiation apparatus, treatment planning unit using this,and particle beam irradiation method that are capable of improving thedetection accuracy with respect to an actual irradiation dose duringtreatment using charged particle beams.

It is a second object of the present invention to provide a particlebeam irradiation apparatus and particle beam irradiation method that arecapable of enhancing the control accuracy with respect to theirradiation dose of charged particle beams.

It is a third object of the present invention to provide a particle beamirradiation apparatus and particle beam irradiation method that arecapable of reliably preventing the excessive irradiation of chargedparticle beams due to a monitor abnormality, input error, or the like.

It is a fourth object of the present invention to provide a particlebeam irradiation apparatus and particle beam irradiation method that arecapable of reliably preventing the excessive irradiation of chargedparticle beams due to a malfunction or the like of a beam stoppingfunction.

It is a fifth object of the present invention to provide a particle beamirradiation apparatus and particle beam irradiation method that arecapable of reducing the treatment time when performing irradiation ofcharged particle beams for each of a plurality of layer regions in atarget.

SUMMARY OF THE INVENTION

To achieve the above-described first object, the present inventionprovides a particle beam irradiation apparatus that includes anaccelerator for extracting a charged particle beam; an beam deliveryapparatus having a charged particle beam scanning unit and outputtingthe charged particle beam extacted from the accelerator; and acontroller that stops the output of the charged particle beam from thebeam delivery apparatus, and that, in a state where the output of thecharged particle beam is stopped, controls the charged particle beamscanning unit to change the irradiation position of the charged particlebeam, start the output of the charged particle beam from the beamdelivery apparatus after the above-described change, and performirradiations of the charged particle beam with respect to at least oneirradiation position a plurality of times based on treatment planninginformation.

In the present invention, the controller controls the charged particlebeam scanning unit to perform irradiations of the charged particle beamwith respect to at least one irradiation position a plurality of times.By virtue of this feature, regarding an irradiation position subjectedto too much irradiation dose by one-time ion irradiation, it is possibleto perform a divided irradiation so as to reduce an irradiation dose foreach radiation. This allows the difference in irradiation dose betweenthe irradiation position subjected to the largest dose and thatsubjected to the smallest dose to be reduced, thereby leveling offirradiation dose. As a result, the capacity of the capacitor of aposition monitor can be correspondingly reduced to enhance theresolution, and therefore, the actual irradiation dose during treatmentcan be detected further correctly.

To achieve the above-described second object, the present inventionprovides a particle beam irradiation apparatus including a controllerthat controls the irradiation of the charged particle beam to theirradiation position so that the irradiation dose applied to theirradiation position becomes a set irradiation dose, in a state wherethe irradiation dose applied to the irradiation position during the timeperiod from the outputting of a beam extraction stop signal at the timewhen the irradiation dose detected by the irradiation dose detectorreaches the set irradiation dose up to the extraction stop of thecharged particle beam from the accelerator, is added.

Even if the beam stop command is inputted, strictly speaking, it is notimpossible that some amount of response delay occurs rather than theextraction of the charged particle beam from the accelerator immediatelystops.

In the present invention, the controller can perform an irradiation ofthe charged particle beam to an irradiation position so that theirradiation dose at the irradiation position becomes a set irradiationdose, in a state where the irradiation dose applied to the irradiationposition during the time period from the outputting of a beam extractionstop signal up to the extraction stop of the charged particle beam fromthe accelerator, is added. This allows the irradiation dose at eachirradiation position to become substantially the set irradiation dose,thereby enabling the charged particle beam to be applied to eachirradiation position with high accuracy. To control the irradiationdose, even if there is time delay between the outputting of the beamextraction stop signal and the extraction stop of the charged particlebeam from the accelerator, the irradiation dose at each irradiationposition can be made to be a set irradiation dose, allowing for theirradiation dose for the time period during the time delay. This makesit possible to irradiate, with high degree of accuracy, any irradiationposition with charged particle beams of a dose substantially equal tothe set irradiation dose.

To achieve the above-described third object, the present inventionprovides a particle beam irradiation apparatus including a controllerthat stops the output of the charged particle beam from the beamdelivery apparatus, that, in a state where the output of the chargedparticle beam is stopped, controls the charged particle beam scanningunit to change the irradiation position of the charged particle beam andto start the output of the charged particle beam from the beam deliveryapparatus after the above-described change, and that determines theoccurrence of an abnormality based on an elapsed time from theirradiation start of the charged particle beam with respect to oneirradiation position.

In the present invention, the controller determines the occurrence of anabnormality based on an elapsed time from the irradiation start of thecharged particle beam with respect to one irradiation position.Therefore, even if the irradiation time of the charged particle beam islikely to abnormally elongate due to the occurrence of a malfunction orfailure of the irradiation dose detector, or an improper input value,the irradiation of the charged particle beam can be stopped after acertain time has elapsed. This reliably prevents an excessiveirradiation to a target, and further improves the safety.

To achieve the above-described fourth object, the present inventionprovides a particle beam irradiation apparatus including a controllerthat stops the output of the charged particle beam from the beamdelivery apparatus, that, in a state where the output of the chargedparticle beam is stopped, controls the charged particle beam scanningunit to change the irradiation position of the charged particle beam andto start the output of the charged particle beam from the beam deliveryapparatus after the above-described change, and that determines theoccurrence of an abnormality using the irradiation dose detected by theirradiation detector and a second set irradiation dose larger thanrespective first set irradiation doses with respect to a plurality ofirradiation positions in the target.

In the present invention, the controller determines the occurrence of anabnormality, using the irradiation dose detected by the irradiation dosedetector and the second set dose larger than respective first set doseswith respect to a plurality of irradiation positions in the target.Therefore, even if, due to a malfunction or the like of the beamstopping function, the charged particle beam does not readily stop andthe irradiation dose is likely to abnormally increase, the irradiationcan be stopped at a certain upper limit irradiation dose, therebyreliably preventing an excessive irradiation to the target. This furtherenhances the safety.

To achieve the above-described fifth object, the present inventionprovides a particle beam irradiation apparatus including a controllerthat performs control to decelerate the charged particle beam in theaccelerator when the irradiation of the charged particle beam withrespect to one of a plurality of layer regions that are different inirradiation energy from each other in a target to be irradiated with thecharged particle beam from the beam delivery apparatus, has beencompleted.

In the spot scanning irradiation according to the present invention, asthe size of a target changes, the number of spots in a layer changes,and consequently, the time required to complete an irradiation to allspots in the layer changes. Regarding the allowable extraction period ofthe synchrotron, if it is set to be long with a large target assumed,the irradiations to all layers takes much time to complete, therebyelongating the treatment time for a patient. In the present invention,after the irradiation in a layer region has been completed, the chargedparticle beam in the accelerator is decelerated, and therefore, theallowable extraction period of the charged particle beams in theaccelerator can be earlier terminated. As a result, even when it isnecessary to irradiate a plurality of layer regions with chargedparticle beams, the treatment time can be made short.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the overall construction of a particlebeam irradiation apparatus according to an embodiment of the presentinvention;

FIG. 2 is a flowchart showing the control procedure executed by thecomputing means of the treatment planning unit shown in FIG. 1;

FIG. 3 is a schematic diagram showing an example of distribution of doseapplied to each layer in order to secure uniformity in an affected area;

FIG. 4 is a diagram illustrating an example of affected area to beirradiated by the particle beam irradiatoin apparatus shown in FIG. 1;

FIG. 5 is a schematic diagram showing an example of distribution of thedose applied to each layer in order to secure uniformity in an affectedarea;

FIG. 6 is a flowchart showing the control procedure executed by thecomputing means of the treatment planning unit shown in FIG. 1;

FIG. 7 is a table showing an example of the number of times of divisionof each layer at the time of irradiation, the number of times ofdivision being planned in the treatment planning unit shown in FIG. 1;

FIG. 8 is a table showing an example of division mode of each layer atthe time of irradiation, the division mode being planned in thetreatment planning unit shown in FIG. 1;

FIG. 9 is a schematic plan view illustrating an example of scanning modeof each layer at the time of irradiation, the scanning mode having beenplanned in the treatment planning unit shown in FIG. 1;

FIG. 10 is a schematic plan view illustrating another example ofscanning mode of each layer at the time of irradiation, the scanningmode having been planned in the treatment planning unit shown in FIG. 1;

FIG. 11 is a table showing the contents of command signals to executethe scanning mode of each layer at the time of irradiation, the commandsignal having been planned in the treatment planning unit shown in FIG.1;

FIG. 12 is a flowchart showing the control procedure executed by thescanning controller, and accelerator and transport system controllershown in FIG. 1;

FIG. 13 is a detailed functional block diagram of the functionalconstruction of the scanning controller shown in FIG. 1;

FIG. 14 is a flowchart showing details of the control procedure executedby the scanning controller shown in FIG. 1;

FIG. 15 is a timing chart illustrating operations of the recordingcounter and preset counter shown in FIG. 13.

FIG. 16 is a timing chart showing an example of operations of a presetcounter and recording counter as well as actual beam operations realizedby the control procedures executed by a preset counter control sectionand recording counter control section shown in FIG. 14;

FIG. 17 is a diagram showing an example of irradiation dose distributionrealized by a comparative example in the present invention, thecomparative example corresponding to the conventional art.

FIG. 18 is a diagram showing an example of irradiation dose distributionrealized by the control procedures executed by the preset countercontrol section and recording counter control section shown in FIG. 14;and

FIG. 19 is a schematic diagram of the overall construction of a particlebeam irradiation apparatus according to another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a particle beam treatment system having a particle beamirradiation apparatus according to an embodiment of the presentinvention will be described with reference to the accompanying drawings.

As shown in FIG. 1, a proton beam treatment system, which is a particlebeam treatment system according to this embodiment, includes a chargedparticle beam generating unit 1 and a beam transport system 4 connectedto the downstream side of the charged particle beam generating unit 1.

The charged particle beam generating unit 1 comprises an ion source (notshown), a pre-stage charged particle beam generating unit (linearaccelerator (linac)) 11, and a synchrotron (accelerator) 12. Thesynchrotron 12 includes a high-frequency applying unit 9 andacceleration unit 10. The high-frequency applying unit 9 is constructedby connecting a high-frequency applying electrode 93 disposed on thecirculating orbit of the synchrotron 12 and a high-frequency powersource 91 by an open/close switch 92. The acceleration unit (secondelement; charged particle beam energy changing unit) 10 comprises ahigh-frequency accelerating cavity (not shown) disposed on thecirculating orbit thereof, and a high-frequency power source (not shown)for applying a high-frequency power to the high-frequency acceleratingcavity. Ions generated in the ion source, e.g., hydrogen ions (protons)or carbon ions, are accelerated by the pre-stage charged particle beamgenerating unit (e.g., linear charged particle beam generating unit) 11.The ion beam (proton beam) emitted from the pre-stage charged particlebeam generating unit 11 is injected into the synchrotron 12. In thesynchrotron 12, this ion beam, which is a charged particle beam, isgiven energy and accelerated by the high-frequency power that is appliedto the ion beam through the high-frequency accelerating cavity from thehigh-frequency power source 91. After the energy of the ion beamcirculating through the synchrotron 12 has been increased up to a setenergy (e.g., 100 to 200 MeV), a high frequency for emission from thehigh-frequency power source 91 reaches the high-frequency applyingelectrode 93 through the open/close switch 92 in a closed state, and isapplied to the ion beam from the high-frequency applying electrode 93.The application of this high-frequency causes the ion beam that iscirculating within a stability limit to shift to the outside of thestability limit, thereby extracting the ion beam from the synchrotron 12through an extraction deflector 8. At the extraction of the ion beam,currents supplied to quadrupole electromagnets 13 and bendingelectromagnets 14 are held at set values, and the stability limit isheld substantially constant. Opening the open/close switch 92 to stopthe application of the high frequency power to the high-frequencyapplying electrode 93, stops the extraction of the ion beam from thesynchrotron 12.

The ion beam extracted from the synchrotron 12 is transported to thedownstream side of the beam transport system 4. The beam transportsystem 4 includes quadrupole electromagnets 18 and a deflectionelectromagnet 17; and quadrupole electromagnets 21 and 22, anddeflection electromagnets 23 and 24 that are sequentially arranged on abeam path 62 communicating with the beam delivery apparatus 15 providedin a treatment room from the upstream side toward the beam travelingdirection. Here, the aforementioned electromagnets each constitute afirst element. The ion beam introduced into the beam transport system 4is transported to the beam delivery apparatus 15 through the beam path62.

The treatment room has the beam delivery apparatus 15 affixed to arotating gantry (not shown) provided therein. A beam transport unithaving an inverse U-shape and including a part of the beam path 62 inthe beam transport system 4, and the beam delivery apparatus 15 aredisposed in a rotating drum (not shown) with a substantially cylindricalshape, of the rotating gantry (not shown). The rotating drum isconfigured so as to be rotated by a motor (not shown). A treatment gauge(not shown) is formed in the rotating drum.

The beam delivery apparatus 15 has a casing (not shown) affixed to therotating drum and connected to the aforementioned inverse U-shaped beamtransport unit. Scanning electromagnets 5A and 5B for scanning a beam, adose monitor 6A, a position monitor 6B and the like are disposed in thecasing. The scanning electromagnets 5A and 5B are used for deflecting abeam, for example, in directions orthogonally intersecting each other(an X-direction and Y-direction) on a plane perpendicular to the beamaxis, and moving an irradiation position in the X-direction andY-direction.

Before an ion beam is applied from the beam delivery apparatus 15, a bed29 for treatment is moved by a bed drive unit (not shown) and insertedinto the aforementioned treatment gauge, and the positioning of the bed29 for irradiation with respect to the beam delivery apparatus 15 isperformed. The rotating drum is rotated by controlling the rotation ofthe motor by a gantry controller (not shown) so that the beam axis ofthe beam delivery apparatus 15 turns toward the affected part of apatient 30. The ion beam introduced into the beam delivery apparatus 15from the inverse U-shaped beam transport unit through the beam path 62is caused to sequentially scan irradiation positions by the scanningelectromagnets (charged particle beam scanning unit) 5A and 5B, andapplied to the affected part (e.g., occurrence region of cancer ortumor) of the patient 30. This ion beam releases its energy in theaffected part, and forms a high dose region there. The scanningelectromagnets 5A and 5B in the beam delivery apparatus 15 arecontrolled by a scanning controller 41 disposed, for example, in thegantry chamber in a treatment unit.

A control system included in the proton beam treatment system accordingto this embodiment will be described with reference to FIG. 1. Thiscontrol system 90 comprises a central control unit 100, storage unit 110storing treatment planning database, scanning controller 41, andaccelerator and transport system controller 40 (hereinafter referred toas an “accelerator controller”). Furthermore, the proton beam treatmentsystem according to this embodiment has a treatment planning unit 140.

While the aforementioned treatment planning data (patient data) storedin the storage unit 110 on a patient-by-patient basis is notparticularly shown, the treatment planning data includes data such aspatient ID numbers, irradiation doses (through a treatment and/or perfraction), irradiation energy, irradiation directions, irradiationpositions, and others.

The central control unit 100 has a CPU and memory 103. The CPU 100 readsthe above-described treatment planning data concerning patients to betreated from the storage unit 110, using the inputted patientidentification information. The control pattern with respect to theexciting power supply to each of the above-described electromagnets isdetermined by the value of irradiation energy out of the treatmentplanning data on a patient-by-patient basis.

The memory 103 stores a power supply control table in advance.Specifically, for example, in accordance with various values ofirradiation energy (70, 80, 90, . . . [MeV]), values of supply excitingpower or their patterns with respect to a quadrupole electromagnet 13and deflection electromagnet 14 in the charged particle beam generatingunit 1 including the synchrotron 12; and the quadrupole electromagnets18, deflection electromagnet 17, the quadrupole electromagnets 21 and22, and deflection electromagnets 23 and 24 in the beam transport system4, are preset.

Also, using the above-described treatment planning data and power supplycontrol table, the CPU 101 as a control information producing unit,produces control command data (control command information) forcontrolling the electromagnets provided on the charged particle beamgenerating unit 1 and the beam paths, regarding a patient to be treated.Then, the CPU 101-outputs the control command data produced in thismanner to the scanning controller 41 and accelerator controller 40.

One of the features of this embodiment lies in that, based on thetreatment planning data created by the treatment planning unit 140, thecentral control unit 100, scanning controller 41, and acceleratorcontroller 40 performs control operations in close liaison with oneanother as follows: (1) they stops the output of an ion beam from thebeam delivery apparatus 150, and in a state where the output of the ionbeam is stopped, they control the scanning electromagnets 5A and 5B tochange the irradiation position (spot) of the ion beam and to start theoutput of the ion beam from the beam delivery apparatus 15 after theaforementioned change (so-called “scanning”); (2) in order to reducevariations in irradiation dose at a spot, they control the synchrotron12 and beam delivery apparatus 15 to divide an irradiation of an ionbeam with respect to at least one identical irradiation position (spot)at which the dose otherwise would exceed a division referenceirradiation dose (discussed below), into a plurality of times ofirradiations.

Hereinafter, detailed explanation thereof will be provided withreference to FIGS. 2 to 18.

First, the creation of a treatment plan by the treatment planning unit140 is explained. The treatment planning unit 140 is, for example,constituted of a personal computer. While its illustration is omitted,the treatment planning unit 140 includes an input unit (e.g., keyboard)which can be operated by an operator and with which the operator caninput; a computing unit (e.g., CPU) that performs a predeterminedarithmetic processing based on an input result by the aforementionedinput means and operation means; an input/output interface that performsthe input/output of information, such as the input of external imagedata and the output of treatment planning data created by this computingunit; and a display unit.

FIG. 2 is a flowchart showing arithmetic processing steps executed bythe aforementioned computing means of the treatment planning unit 140.In FIG. 2, if an operator (usually a doctor or medical staff) inputsidentification information (e.g., a name, ID number) about a patient tobe treated via the input unit, the determination in step 101 issatisfied, and the processing advances to step 102, where a patientimage file (file previously taken by extra imaging means such as CTscanner and stored in the database of the storage unit 110) of apertinent patient is read. Here, the patient image file is tomographyimage information.

Thereafter, in step 103, the read patient image file is outputted on adisplay unit as display signals, and a corresponding display is made. Ifthe operator performs specification by filling in a target region to beirradiated with an ion beam via the input unit while watching thedisplayed patient image file, the determination in step 104 issatisfied, and the processing advances to step 105, where recognitionprocessing is three-dimensionally performed regarding the filled-inregion.

In this situation, if the operator inputs a target dose to be applied toa corresponding target region via the input unit, the determination instep 106 is satisfied. Furthermore, if the operator inputs anirradiation direction of the ion beam, the determination in step 107 issatisfied, and the processing advances to step 108. Moreover, if theoperator inputs, via the input unit, a division reference irradiationdose, which is a reference irradiation dose such that a dividedirradiation is to be performed if an irradiation dose per unit spotexceeds this reference irradiation dose, the determination in step 108is satisfied, and the processing advances to step 110.

Here, description will be made of the relationship between the depth ofa target and energy of an ion beam. The target is a region, including anaffected part, to be irradiated with an ion beam, and is somewhat largerthan the affected part. FIG. 3 shows the relationship between the depthof the target in a body and the irradiation dose of ion beam. The peakof dose as shown in FIG. 3 is referred to as a “Bragg peak”. Theapplication of an ion beam to the target is performed in the position ofthe Bragg peak. The position of Bragg peak varies depending on theenergy of ion beam. Therefore, dividing the target into a plurality oflayers (slices) in the depth direction (traveling direction of ion beamin the body), and changing the energy of ion beam to the energy incorrespondence with a depth (a layer) allows the ion beam to beirradiated throughout the entire target (target region) having athickness in the depth direction as uniformly as possible. From thispoint of view, in step 110, the number of layers in the target region tobe divided in the depth direction is determined. One possibledetermination method for determining the number of layers is to set thethickness of a layer, and to automatically determine the number oflayers in accordance with the aforementioned thickness and a thicknessof the target region in the depth direction. The thickness of layer maybe a fixed value irrespective of the size of the target region, oralternatively may be automatically determined appropriately to themaximum depth of the target region. Still alternatively, the thicknessof layer may be automatically determined in accordance with the spreadof the energy of ion beam, or simply, the number itself of layers may beinputted by the operator via the input unit instead of determining thethickness of layer.

FIG. 4 is a diagram showing an example of layers determined in theabove-described manner. In this example, the number of layers is four:layers 1, 2, 3, and 4 in this order from the lowest layer. The layers 1and 2 each have a spread of 10 cm in the X-direction and a spread of 10cm in the Y-direction. The layers 3 and 4 each have a spread of 20 cm inthe X-direction and a spread of 10 cm in the Y-direction. FIG. 3represents an example of dose distribution in the depth direction asviewed from the line A-A′ in FIG. 4. On the other hand, FIG. 5represents an example of dose distribution in the depth direction asviewed from the line B-B′ in FIG. 4.

After the number of layers has been determined in this manner, theproceeding advances to step 111, where the number (and positions) ofspots that divide each layer (target cross section) in the directionperpendicular to the depth direction, is determined. On thisdetermination, like the above-described layers, one spot diameter isset, and the number of spots is automatically determined in accordancewith the size of the spot and the size of the pertinent layer. The spotdiameter may be a fixed value, or alternatively may be automaticallydetermined appropriately to the target cross section. Stillalternatively, the spot diameter may be automatically determinedappropriately to the size of ion beam (i.e., the beam diameter), orsimply, spot positions themselves or the distances themselves betweenspot positions may be inputted by the operator via the input unitinstead of determining the spot size. After step 111 has been completed,the processing advances to step 120, where the irradiation dose at eachspot in all layers is determined.

FIG. 6 is a flowchart showing detailed procedure in the aforementionedstep 120. As described above, basically, the application of an ion beamto the target is performed in the position of the Bragg peak, and it isdesirable that the ion beam be irradiated throughout the entire target(target region) having a thickness in the depth direction as uniformlyas possible. On the determination in the irradiation dose at each spot,therefore, it is necessary to ultimately secure a uniform irradiationthroughout the entire target region. In light of the above, in steps121-123, firstly initial condition are determined in step 121.Specifically, by the accumulation of past calculation examples, theutilization of simple models or the like, the irradiation doses withrespect to all spots on layer-by-layer basis that are deemed tocorrespond to the target doses, the irradiation direction of ion beam,and the numbers of layers that were inputted or determined in steps 106to 111, are determined as temporary values.

Thereafter, the processing advances to step 122, where, using a knownmethod, a simulation calculation is performed as to how the actual dosedistribution in the entire target region becomes, if an irradiation isperformed using the values of irradiation doses with respect to allspots, the doses having been determined in step 121. Then, in step 123,it is determined whether the aforementioned calculated dose distributionis uniform throughout substantially the entire region of the target,namely, whether variations remain within a given limit. If not so, theprocessing advances to step 124, where a predetermined correction ismade. This correction may be such that the irradiation doses at spotssomewhat outstandingly higher/lower than an average dose value areautomatically lowered/raised with a correction width, and that thecorrection width may be set by a manual operation. After such acorrection, the processing returns to step 121 and the same procedure isrepeated. Therefore, the correction in step 124 and the dosedistribution calculation in step 122 are performed until the irradiationdose distribution becomes uniform to a certain extent. Thus, ultimately,the irradiation doses with respect all spots that allow substantiallyuniform dose distribution to be implemented in the entire target region,are determined. Thereafter, the processing advances to step 130.

In this stage, although the irradiation doses to all spots have eachbeen determined, each of all these spots is set to be irradiated with apertinent allocated irradiation dose at one time. In step 130, if thereare any irradiation doses exceeding the division reference irradiationdose inputted before in step 108, out of the irradiation dosesdetermined with respect to all spots, the ion beam irradiation to eachof such spots is not performed at one time, but is performed in the formof irradiations divided into a plurality of times (at least two times).Here, we assume the number N of irradiations to be a minimum naturalnumber n that satisfies the relationship: n≧R/Rs, where R and Rs,respectively, denote the irradiation dose and the division referenceirradiation dose at a pertinent spot. In other words, the number N ofirradiations is assumed to be a value obtained by rounding-up thedecimal places of R divided by Rs. Therefore, if N=1, then R≦Rs, andhence a plurality of times of divided irradiations are not performed(namely, the irradiation is performed at one time). If N=2, then R>Rs,and hence it is planned that irradiations divided into a plurality oftimes are performed.

FIG. 7 shows an example (layers 1 to 4) of divided irradiations asdescribed above with reference to FIGS. 4 and 5. In this example, thedivision reference dose is assumed to be 10 (a relative value withoutunit; the same shall apply hereinafter). As shown in FIG. 7, regardingthe layer 1, before division processing (i.e., when the irradiation isperformed at one time), the irradiation dose at each spot was 70. Suchbeing the situation, it is planned that irradiations divided into seventimes are performed, the irradiation dose for each divided irradiationbeing 10. Likewise, regarding the layers 2, 3, and 4, the irradiationdoses at each spot before division processing were 25, 17.9, and 12.6,respectively. Accordingly, in the layers 2, 3, and 4, respectively, itis planned that irradiations divided into three, two, and two times wereperformed, the irradiation dose for each divided irradiation being 8.3,9, and 6.3, respectively.

More specific explanations of the above will be provided with referenceto FIG. 8. As described above, regarding the layer 1 (the regioncorresponding to the right half of the layer 1 shown in FIG. 8; here,the right-left direction in FIG. 8 corresponds to that in FIG. 4),irradiations divided into seven times are performed, and it is plannedthat an irradiation with irradiation dose of 10 is repeated in each ofthe first-time to seventh-time irradiations. Regarding the layer 2 (theregion corresponding to the right half of the layer 2 shown in FIG. 8),it is planned that an irradiation with irradiation dose of 8.3 isrepeated three times. Regarding the layer 3, with respect to the regionshown in the right half in FIG. 8, it is planned that an irradiationwith irradiation dose of 9.0 is repeated two times, while with respectto the region shown in the left half in FIG. 8, it is planned that anirradiation with irradiation dose of 10 is repeated seven times.Regarding the layer 4, with respect to the region shown in the righthalf in FIG. 8, it is planned that an irradiation with an irradiationdose of 6.3 is repeated two times, while with respect to the regionshown in the left half in FIG. 8, it is planned that an irradiation withirradiation dose of 8.3 is repeated three times.

After step 130 has been completed, the processing advances to step 131,where the order of the irradiation with respect to spots in each of thelayers is determined. Specifically, in the proton beam treatment systemaccording to this embodiment, as described above, the output of an ionbeam from the beam delivery apparatus 15 is stopped, and in the statethe output of the ion beam is stopped, a scanning irradiation to changethe irradiation position (spot) is performed. In step 131, it isdetermined how the ion beam is to be moved with respect to each spot inthe scanning irradiation. Here, the ion beam to be applied to the targetis narrow, and its diameter is a little larger than that of the spotdiameter.

FIGS. 9 and 10 each show an example of the setting of the order of spotirradiation. This order of spot irradiation order corresponds to theexample described with reference to FIGS. 4, 3, 5, 7, and 8.

FIG. 9 shows the setting of irradiation orders in both the layers 1 and2 in a combined and simplified manner. As shown in FIG. 9, for each ofthe layers 1 and 2, 100 spots in total are set in a lattice shape of 10rows and 10 columns. The application of an ion beam to the target (thesquare region in FIG. 9) of the layers 1 and 2 is performed, forexample, in a manner as follows: an irradiation is performed on aspot-by-spot basis from one end (the left lower corner in FIG. 9) in thespot row (including ten spots) situated at one end of these layerstoward the other end (the right lower corner in FIG. 9) of this spotrow, i.e., from the left toward the right in FIG. 9. After theirradiation to the other end has been completed, the irradiation isperformed on a spot-by-spot basis from one end (the right lower end inFIG. 9) in another spot row adjacent to the aforementioned spot rowtoward the other end (the left end in FIG. 9) of the other row, i.e.,from the right toward the left in FIG. 9. After the irradiation to theother end in the other row has been completed, the ion beam moves to anext other spot row adjacent. In this manner, in this embodiment, it isplanned that, in the horizontal surface of each of the layers 1 and 2,the ion beam is moved by inversing its traveling direction (i.e., bycausing the ion beam to meander) for each of the adjacent spot rows,until the ion beam reaches the last spot (the left upper corner in FIG.9) in the last spot row, thus completing an irradiation operation (oneof a plurality of times of scanning operations) with respect to thelayers 1 and 2. Regarding the layer 1, the irradiation dose at each ofthe total of 100 spots is 10 for each divided irradiation, and asdescribed above, one meandering scanning operation for each of the spotrows is repeated seven times. From the first-time through seventh-timescanning operations, the same irradiation order setting may be applied.Alternatively, however, in order to speed up an irradiation, forexample, the second-time scanning may be performed from the left uppercorner toward the left lower corner in FIG. 9 along the reverse route(the same shall apply hereinafter). Also, regarding the layer 2, asdescribed with reference to FIG. 8, it is planned that the irradiationdose at each of the total of 100 spots is 8.3 for each dividedirradiation, and it is planned that one meandering scanning operation asdescribed above is repeated three times.

FIG. 10 shows the setting of irradiation orders in both the layers 3 and4 in a combined and simplified manner, although this is an example ofthe first-time and second-time scanning operations. As shown in FIG. 10,for each of the layers 1 and 2, 200 spots in total are set in a latticeshape of 10 rows and 20 columns. The application of an ion beam to thetarget (the rectangular region in FIG. 9) of the layers 3 and 4 isperformed, as is the case with the layers 1 and 2, for example, in amanner as follows: an irradiation is performed on a spot-by-spot basisfrom one end (the left lower corner in FIG. 10) in the spot row(including twenty spots) situated at one end of these layers towardanother end (the right lower corner in FIG. 10) in this spot row. Afterthe irradiation to the other end has been completed, the irradiation isperformed from one end (the right lower end in FIG. 10) in another spotrow adjacent to the aforementioned spot row toward the other end (theleft end in FIG. 10) of the other row. After the irradiation to theother end in the other row has been completed, the ion beam moves to anext other spot row adjacent. In this way, in this embodiment, also foreach of the layers 3 and 4, it is planned that, in the horizontalsurface, the ion beam is moved by causing the ion beam to meander foreach of the adjacent spot rows, and that one irradiation operation (oneof two scanning operations) with respect to the layers 3 and 4 iscompleted.

In the layer 3, as shown in FIG. 8, the irradiation dose for eachdivided irradiation with respect to each of the total of 200 spots is 9for each of the 100 spots in the right half region in FIG. 10, and 10for each of the 100 spots in the left half region in FIG. 10. It isplanned, therefore, that one scanning operation that meanders for eachof the spot rows while changing an irradiation dose at a midpoint in aspot row, is repeated two times. Likewise, in the layer 4, theirradiation dose for each divided irradiation with respect of each ofthe total of 200 spots is 6.3 for each of the 100 spots in the righthalf region in FIG. 10, and 8.3 for each of the 100 spots in the righthalf region in FIG. 10. It is planned, therefore, that one scanningoperation that meanders for each of the spot rows while changing anirradiation dose at a midpoint in a spot row, is repeated two times.

Regarding each of the layers 3 and 4, in irradiations at the third timeand afterward, the irradiation to the 100 spots in the right half inFIG. 10 do not need, and the irradiation to the 100 spots in the lefthalf alone is performed (see FIG. 8). Regarding the irradiation orderthen, although it is not particularly illustrated, for example,performing like the layers 1 and 2 shown in FIG. 9 suffices for thelayers 3 and 4. Regarding the layer 3, the irradiation dose with respectof each of its 100 spots is 10 for each divided irradiation, and it isplanned that in the left half region alone, for example, one meanderingscanning operation is performed five times (in the third-time toseventh-time scanning operations). Likewise, in the layer 4, theirradiation dose with respect of each of its 100 spots is 8.3 for eachdivided irradiation, and it is planned that in the left half regionalone, for example, one meandering scanning operation is performed (inthe third-time scanning).

After the spot irradiation order has been determined as described above,the processing advances to step 132, where the dose distribution at atarget area that is estimated when irradiations are performed with theirradiation dose with respect to all layers and all spots and in thespot irradiation order that were each determined as described above, iscalculated using a known method. This simulation uses a method withhigher accuracy and requiring a little longer calculation time than asimplified method as shown before in FIG. 6. Hereafter, the processingadvances to step 133, where the estimated dose distribution resultcalculated in step 132 is outputted on the display unit as displaysignals, together with a planning result. The display then may be, forexample, a summary including a dose volume histogram (DVH) or the like.Preferably, a comment about influences on normal organs, and others canbe displayed together.

If the operator determines that this display is insufficient (improper)upon watching this display, he/she does not input “OK”, and hence, theprocessing returns to step 107 based on the determination by step 134.Until the determination in step 134 becomes “YES”, the processing ofsteps 107 to 134 is repeated.

If the operator determines that the created treatment planninginformation is proper, he/she inputs “OK”, thereby satisfying thedetermination in step 134. Thereafter, the operator performs aregistration instruction input (via a button on the screen display orkeyboard) to permit the registration in the treatment planninginformation, thereby satisfying the determination in step 135. Then, ina next step 136, the operator performs registration processing for thetreatment planning information at the storage unit 110, thus completingthe processing shown in FIG. 2.

Next, the central control unit 100 reads the treatment planninginformation, in which divided irradiations are planned as describedabove and which has been stored in the storage unit 110, and stores itinto the memory 103. The CPU 101 transmits, to the memory 41M of thescanning controller 41, the treatment planning information stored in thememory 103 (i.e., information such as the number of layers, the numberof irradiation positions (the numbers of spots), the irradiation orderwith respect to irradiation positions in each of the layers, a targetirradiation dose (set irradiation dose) at each irradiation position,and current values of the scanning electromagnets 5A and 5B with respectto all spots in each of the layers). The scanning controller 41 storesthis treatment planning information into the memory 41M. Also, the CPU101 transmits, to the accelerator controller 40, all data ofacceleration parameters of the synchrotron 12 with respect to all layersout of the treatment planning information. The data of accelerationparameters includes the value of an exciting current for each of theelectromagnets for the synchrotron 12 and beam transport system, and thevalue of high-frequency power to be applied to the high-frequencyaccelerating cavity, which are each determined by the energy of ion beamapplied to each of the layers. The data of these acceleration parametersis classified, for example, into a plurality of acceleration patterns inadvance.

FIG. 11 shows a part of the treatment planning information stored in thememory 41M of the scanning controller 41. The part of the informationcomprises irradiation parameters, that is, information on theirradiation index number (layer number and irradiation number),information on the X-direction position (X-position) and the Y-directionposition (Y-position) of an irradiation position (spot), and informationon a target irradiation dose (irradiation dose) for each dividedirradiation. Furthermore, the irradiation parameters includes layerchange flag information. The information on the irradiation number, forexample, “2-2” means a “second-time irradiation in the layer 2, “2-3”means a “third-time irradiation in the layer 2”, and “3-1” means a“first-time irradiation in the layer 3”. The information on aX-direction position and Y-direction position is represented by currentvalues of the scanning electromagnets 5A and 5B for scanning an ion beamto the irradiation position specified by the pertinent X-position andY-position. Spot numbers j (described later) are given, in theirradiation order, to all divided irradiations with respect to the layer2, i.e., “2-1” (not shown), “2-2”, and “2-3”. Likewise, spot numbers aregiven to all divided irradiations with respect to the other layers 1, 3,and 4.

Next, with reference to FIG. 12, specific descriptions will be made ofrespective controls by the scanning controller 41 and the acceleratorcontroller 40 in performing the spot scanning in this embodiment. If anirradiation start instructing unit (not shown) disposed in the treatmentroom is operated, then in step 201, the accelerator controller 40correspondingly initializes an operator i denoting a layer number to 1,as well as initializes an operator ; denoting a spot number to 1, andoutputs signals to that effect.

Upon being subjected to the initialization in step 201, the acceleratorcontroller 40 reads and sets the accelerator parameters with respect tothe i-th layer (i=1 at this point in time) out of the accelerationparameters of a plurality of patterns stored in the memory, in step 202.Then, in step 203, the accelerator controller 40 outputs it to thesynchrotron 12. Also, in step 203, the accelerator controller 40 outputsexiting current information with respect to the electromagnets that isincluded in the i-th accelerator parameters, to the power source foreach of the electromagnets of the synchrotron 12 and beam transportsystem 5, and controls a pertinent power source so that each of theelectromagnets is excited by a predetermined current using this exitingcurrent information. Furthermore, in step 203, the acceleratorcontroller 40 controls the high-frequency power source for applying ahigh-frequency power to the high-frequency cavity to increase thefrequency up to a predetermined value. This allows the energy of an ionbeam circulating through the synchrotron 12 to increase up to the energydetermined by the treatment plan. Thereafter, the processing advances tostep 204, where accelerator controller 40 outputs an extractionpreparation command to the scanning controller 41.

Upon receipt of the information on initial setting in step 201 and theextraction preparation command in step 204 from the acceleratorcontroller 40, in step 205, the scanning controller 41 reads and setscurrent value data and irradiation dose data of the j-th spot (j=1 atthis point in time) out of the current value data (data shown in the“X-position and Y-position” columns in FIG. 11) and the irradiation dosedata (data shown in the “irradiation dose” column in FIG. 11), which arealready stored in the memory 41M as described above (see FIG. 13 shownlater). Similarly, regarding the aforementioned target count numberstored in the memory 41M, the scanning controller 41 reads and sets dataof the j-th spot (j=1 at this point in time) as well. Here, the scanningcontroller 41 controls a pertinent power so that the electromagnets 5Aand 5B are excited by the current value of the j-th spot.

After the preparation for the irradiation to the pertinent spot has beencompleted in this manner, the scanning controller 41 outputs a beamextraction start signal in step 300, and controls the high-frequencyapplying unit 9 to extract an ion beam from the synchrotron.Specifically, the open/close switch 92 is closed by the beam extractionstart signal passing through the accelerator controller 40 and a highfrequency is applied to the ion beam, whereby the ion beam is extracted.Because the electromagnets 5A and 5B are excited so that the ion beamreaches the first spot position, the ion beam is applied to the firstspot in a pertinent layer by the beam delivery apparatus 15. When theirradiation dose at the first spot reaches a pertinent targetirradiation dose, the scanning controller 41 outputs a beam extractionstop signal in step 300. The beam extraction stop signal passes throughthe accelerator controller 40 and opens the open/close switch 92,thereby stopping the extraction of the ion beam.

At this point in time, only the first-time irradiation to the first spotin the layer 1 has been completed. Since the determination in step 208is “No”, the processing advances to step 209, where 1 is added to thespot number j (i.e., the irradiation position is moved to the next spotadjacent). Then, the processing of steps 205, 300, and 208 are repeated.Specifically, until the irradiation to all spots in the layer 1 iscompleted, the irradiation (scanning irradiation) of ion beam isperformed while moving the ion beam to adjacent spots one after anotherby the scanning electromagnets 5A and 5B and stopping the irradiationduring movement.

If all divided irradiations to all spots in the layer 1 (seven-timeirradiations in the above-described example) have been completed, thedetermination in step 208 becomes “Yes”. At this time, the scanningcontroller 41 outputs a layer change command to the CPU of theaccelerator controller 40. Upon receipt of the layer change command, theCPU of the accelerator controller 40 adds 1 to the layer number i (i.e.,changes the object to be irradiated to the layer 2) in step 213, andoutputs a remaining beam deceleration command to the synchrotron 12 instep 214. By the output of the remaining beam deceleration command, theaccelerator controller 40 controls the power source for each of theelectromagnets in the synchrotron 12 to gradually reduce the excitingcurrent of each of the electromagnets until it becomes the predeterminedcurrent such as the current appropriate for the beam injection from thepre-stage accelerator. This decelerates an ion beam circulating throughthe synchrotron 12. As a result, the time period during which a beam canbe extracted varies depending on the number of spots and irradiationdose. At the point in time, since only the irradiation with respect tothe layer 1 has been completed, the determination in step 215 becomes“No”. In step 202, the accelerator parameters for the second layer(layer 2) is read from the memory for the accelerator controller 40 andis set. Hereinafter, the processing of steps 203 to 215 is performedwith respect to the layer 2. Also, until all divided irradiations to allspots in the layer 4 is completed, the processing of steps 202 to 215 isperformed.

If the determination in step 215 becomes “Yes” (i.e., if predeterminedirradiations to all spots in all layers in the target of a patient 30have been completed), the CPU of the accelerator controller 40 outputsan irradiation end signal to the CPU 101.

As described above, under the acceleration by the synchrotron 12, an ionbeam extracted from the synchrotron 12 is transported through the beamtransport system. Then, the ion beam is applied to the target of thepertinent patient in an optimum mode as planned by a treatment plan, viathe beam delivery apparatus 15 in the treatment room in which thepatient to be irradiated is present.

At this time, a detection signal of the dose monitor 6A provided in thenozzle of the beam delivery apparatus 15 is inputted to the scanningcontroller 41. Other features of this embodiment are: by using thisdetection signal, (1) to clear the integrated value of irradiation dosessimultaneously with a beam-off signal; (2) to determine the occurrenceof an abnormal operation in accordance with an elapsed time after beamextraction is started; and (3) to determine the occurrence of anabnormal operation based on the comparison between the integrated valueof irradiation doses and a predetermined regulated value.

More detailed explanations thereof will be provided below with referenceto FIGS. 13 to 18.

FIG. 13 is a detailed functional block diagram showing the functionalconstruction of the scanning controller 41. As shown in FIG. 13, thescanning controller 41 comprises a preset counter 41 a, recordingcounter 41 b, and maximum dose counter 41 c as ones related to thedetection of an irradiation dose, and for controlling these counters,comprises a preset counter control section 41A, recording countercontrol section 41B, and maximum dose counter control section 41C. Here,the dose monitor 6A is a known one, and of a type that outputs pulses inaccordance with the amount of electrical charges ionized by the passageof beam. Specifically, the dose monitor 6A outputs one pulse for eachpredetermined minute charge amount. The preset counter 41 a andrecording counter 41 b determine the irradiation dose by counting thenumber of pulses outputted from the dose monitor 6A.

Besides the above-described preset counter 41 a, the preset countercontrol section 41A includes a spot timer 41Aa, difference calculatingsection 41Ab, determination section 41Ac, OR circuits 41Ad and 41Ae. Thepreset counter 41 a includes a pulse input section 41 aa, set valueinput section 41 ab, initialization (clear) signal input section 41 ac,operation start (START) signal input section 41 ad, count value readingsection 41 ae, and set value comparison result output section 41 af.

Besides the above-described recording counter 41 b, the recordingcounter control section 41B includes a first delay timer 41Ba, seconddelay timer 41Bb, first register 41Bc, second register 41Bd, differencecalculating section 41Be, determination section 41Bf, NOT circuit 41Bg,and OR circuit 41Bh. The recording counter 41 b includes a pulse inputsection 41 ba, initialization (clear) signal input section 41 bc,operation start (START) signal input section 41 bd, and count valuereading section 41 be.

As described above, the maximum dose counter control section 41C has amaximum dose counter 41 c, which includes a pulse input section 41 ca,set value input section 41 cb, initialization (clear) signal inputsection 41 cc, operation start (START) signal input section 41 cd, andset value comparison result output section 41 cf.

Furthermore, the scanning controller 41 has a memory 41M and beamextraction start/stop signal producing section 41S.

FIG. 14 is a flowchart showing the detailed procedures in steps 205 and300 in FIGS. 12 executed by the scanning controller 41 with the abovefeatures. As described above, the operator i is initialized to 1, andthe operator j is initialized to 1, in advance. In step 301, thescanning controller 41 outputs a preset count setting commandcorresponding to the target count number of the preset counter 41 aalready stored in the memory 41M, to the preset counter set value inputsection 41 ab of the preset counter control section 41A. In step 302,the scanning controller 41 sets a target count number at the first spotin the layer 1 in accordance with the aforementioned set command. Here,the “target count number” refers to a value corresponding to the targetirradiation dose of a pertinent spot in a pertinent layer in the column“radiation dose” shown in FIG. 11. This target count number iscalculated by the scanning controller 41 based on the above-describedtarget irradiation dose, before the start of ion beam irradiation. Thecalculation of the target count number using the target irradiation dosemay be performed immediately after the preset counter control section41A receives the aforementioned set command, or alternatively may beperformed before the central control unit 100 transmits data to thescanning controller 41 if the central control unit 100 performs thecalculation. Likewise, at this time, the scanning controller 41 outputsa maximum spot or layer dose counter setting command corresponding tothe target count number (maximum dose count number) of the maximum dosecounter 41 c stored in the memory 41M, to the maximum dose counter setvalue input section 41 cb of the maximum dose counter control section41C. More details thereof will be described later.

Upon completion of step 301, the processing advances to step 303, wherethe scanning controller 41 outputs a current setting command withrespect to the electromagnets 5A and 5B regarding a pertinent spot,i.e., current data corresponding to each of X-position and Y-position inFIG. 11, to the power source for the electromagnets 5A and 5B. Theelectromagnets 5A and 5B generate a deflection electromagnetic forcewith pertinent current values, and output a current setting completionsignal indicating that such a state has been accomplished, to thescanning controller 41. In step 304, this current setting completionsignal is inputted to the beam extraction start/stop signal producingsection 41S.

On the other hand, in the preset counter control section 41A, when thetarget count number is set in step 302 as described above, this setvalue is inputted not only to the aforementioned preset counter setvalue input section 41 ab but also to the difference calculation section41Ab. Furthermore, the count number counted at this point in time (i.e.,the count number at setting) is read from the preset counter count valuereading section 41 ae, and this is also inputted to the differencecalculation section 41Ab. The difference calculation section 41Abcalculates the difference between these values: (count number atsetting)—(target count number), and inputs it to the determinationsection 41Ac. In step 302A, the determination section 41Ac determineswhether this difference is negative, namely, whether the count value atsetting is less than the target count number. If this determination issatisfied, the determination section 41Ac outputs a target count numbersetting OK signal to the beam extraction start/stop signal producingsection 41S.

In step 305, the scanning controller 41 outputs a beam extraction(radiation) start signal from the beam extraction start/stop signalproducing section 41S on the conditions that the target count numbersetting OK signal from the determination section 41Ac of the presetcounter control section 41A, the current setting command in step 303,and the current setting completion signal from the scanningelectromagnets 5A and 5B have been inputted. The beam extraction startsignal passes through the accelerator controller 40 and closes theopen/close switch 92. An ion beam is extracted from the synchrotron 12,and the ion beam is applied to a pertinent spot (e.g., the first spot inthe layer 1). Next, the processing advances to step 306, where the beamextraction start/stop signal producing section 41S outputs a timer startcommand signal for starting the spot timer 41Aa of the preset countercontrol section 41A. If the elapsed time after this start that ismeasured by the spot timer 41Aa becomes a predetermined set time ormore, (namely, if the beam extraction is performed for a predeterminedtime or more without being reset, as described later), a time excesssignal is issued in step 307. In step 308, on the conditions that thetime exceed signal has occurred and the timer start command signal hasbeen inputted, a first abnormality signal is outputted to the centralcontrol unit 100. Upon receipt of the first abnormality signal, thecentral control unit 100 performs a predetermined abnormalityprocessing, for example, an immediate forced stop with respect to beamextraction from the synchrotron 12, and recording to that effect throughthe intermediary of the scanning controller 41 and acceleratorcontroller 41 (or alternatively, not through the intermediary thereof).

On the other hand, when a beam irradiation is started by the output ofthe beam extraction start signal in step 305, detection signal of thedose monitor 6A is converted into a train of dose pulses by acurrent-frequency converter (i.e., I-F converter; not shown), andthereafter they are inputted to the preset counter pulse input section41 aa, recording counter pulse input section 41 ba, maximum dose counterpulse input section 41 ca of the scanning controller 41. These counters41 a, 41 b, and 41 c simultaneously count the pulses. This count numberrepresents the irradiation dose from the start of counting.

If the count value based on the input pulses from the pulse inputsection 41 aa becomes a value of no less than the set value of thetarget count number set in step 302, the preset counter 41 a issues anirradiation dose excess signal in step 309. In step 310, on theconditions that the irradiation dose excess signal has occurred and thetarget count number set in step 302 has been inputted, the presetcounter 41 a outputs a trigger signal from the set value comparisonresult output section 41 af. As a first reset signal, this triggersignal is inputted to the initialization (clear) signal input section 41ac and operation start (START) signal input section 41 ad of the presetcounter 41 a via the OR circuits 41Ad and 41Ae, and in step 311, thecount number of the preset counter 41 a is reset to start recounting.

In step 312, based on the above-described trigger signal, the beamextraction start/stop signal producing section 41S of the scanningcontroller 41 produces a beam extraction start/stop signal and outputsit to the accelerator controller 40. The beam extraction start/stopsignal passes through the accelerator controller 40 and reaches theopen/close switch 92. Substantially by the beam extraction start/stopsignal, the scanning controller 41 controls the open/close switch 92 toopen. This stops the extraction of the ion beam from the synchrotron 12,and stops application of the ion beam to a patient. With the stoppage ofthe irradiation, the beam extraction start/stop signal producing section41S outputs a command signal to stop or reset the spot timer 431Aa instep 313.

The recording counter control section 41B of the scanning controller 41has a first and second delay timers 41Ba and 41Bb. In step 314, theabove-described beam extraction start/stop signal outputted by the beamextraction start/stop signal producing section 41S is inputted as acommand signal for starting the first delay timer 41Ba in the form ofconverting beam ON-OFF switching into OFF-ON switching via the NOTcircuit 41Bg. If the elapsed time after this start becomes apredetermined set time (i.e., first delay time, corresponding to the“delay” in FIG. 16 shown later), a first time arrival signal is sent tothe first register 41Bc of the recording counter control section 41B, instep 315. In step 316, on the conditions that the first time arrivalsignal and a first delay timer start command signal have been inputted,a recording counter reading signal is outputted from the first register41Bc to the recording counter 41Bc, and the count value then is inputtedfrom the recording counter count value reading section 41 be to thefirst register 41Bc. While not shown in FIG. 14 for the sake ofsimplification, the above-described time arrival signal is inputted as asignal for starting the second delay timer 41Bb. As in the case of thefirst delay timer, if the elapsed time after the start becomes apredetermined set time (i.e., a second delay time), a second timearrival signal is sent to the second register 41Bd of the recordingcounter control section 41B. On the conditions that the second timearrival signal and second delay timer start command signal have beeninputted, a recording counter reading signal is outputted from thesecond register 41Bd to the recording counter 41 b, and the count valuethen is inputted from the recording counter count value reading section41 be to the second register 41Bd.

The count values at the first and second registers 41Bc and 41Bd areinputted to the difference calculation section 41Be, and after thedifference therebetween is calculated, the difference is inputted to thedetermination section 41Bf.

In step 317, the determination section 41Bf of the recording countercontrol section 41B determines whether the recording count value is anormal value, i.e., whether the above-described difference is within apredetermined proper range, and if the determination section 41Bfdetermines that the difference is an abnormal value, it outputs a secondabnormality signal to the central control unit 100 in step 318. Uponreceipt of the second abnormality signal, the central control unit 100executes the predetermined abnormality processing as described above. Ifit is determined that the difference is a normal value in step 317, thedetermination section 41Bf inputs a second reset signal for resettingthe recording counter 41 b to the initialization (clear) signal inputsection 41 bc and operation start (START) signal input section 41 bd ofthe recording counter 41 b via the OR circuit 41Bb, and after theresetting, starts recounting in step 319. Also, the count value then isoutputted as an actual dose record from the determination section 41Bfto the central control unit 100. Furthermore, in step 320, thedetermination section 41Bf outputs a third reset signal for resettingthe maximum dose counter control section 41C to the initialization(clear) signal input section 41 cc and operation start (START) signalinput section 41 cd of the maximum dose counter 41 c via the OR circuit41Bb.

On the other hand, based on the third reset signal inputted to theinitialization (clear) signal input section 41 cc and operation start(START) signal input section 41 cd, the maximum dose counter 41 c clearsthe count value and then starts recounting in step 321. If the beamextraction start signal is outputted in step 305, the maximum dosecounter 41 c counts pulses as a detection signal of the dose monitor 6Ainputted to the pulse input section 41 ca of the maximum dose counter 41c. This counter number represents the irradiation dose from the start ofcounting. In this time, in step 323, the maximum dose counter 41 c hasset a target count number (maximum dose count number) in a pertinentspot to be irradiated, in accordance with a maximum dose counter settingcommand inputted to the set value input section 41 cb in theabove-described step 301. If the above-described integrated value ofirradiation dose becomes a value of no less than the set value of thetarget maximum count number set in the above step 323, the maximum dosecounter 41 c produces a count excess signal in step 322. Then, in step324, on the conditions that the set target maximum count number (step323) and the count excess signal has been inputted, the maximum dosecounter 41 c outputs a third abnormality signal from the set valuecomparison result output section 41 cf to the central control unit 100in step 324. Upon receipt of the third abnormality signal, the centralcontrol unit 100 executes the above-described predetermined abnormalityprocessing. The target maximum count number refers to an irradiationdose set so as to be a little larger than the largest target dose inrespective target irradiation doses with respective to all irradiationpositions (all spots) in a target.

FIG. 15 is a timing chart showing a series of operations of the presetcounter 41 a and recording counter 41 b as described above.

According to the particle beam treatment system of this embodiment withthe above-described features, the following effects are provided.

(1) Resolution Enhancing Effect by Divided Irradiations

In general, the position monitor 6B is of a type that accumulateselectric charges ionized by the passage of an ion beam in a capacitorand that reads a voltage induced in the capacitor after the spotirradiation. The capacity of this capacitor is determined so as topermit the amount of ionized electric charges by the spot subjected tothe maximum irradiation dose. Regarding this capacitor, as the capacitydecreases, the output voltage increases and the signal-to-noise ratiobecomes higher, thereby enhancing the position measurement resolution.Conversely, as the capacity increases, the resolution decreases.

Accordingly, in this embodiment, in a treatment plan using the treatmentplanning unit 140, it is planned that the irradiation to each spot in alayer is performed by dividing it into a plurality of times ofirradiations (for example, in the example shown in FIG. 7, irradiationsare performed seven times in the layer 1, three times in the layer 2,two times in the layer 3, and two times in the layer 4). The centralcontrol unit 100, accelerator controller 40, and scanning controller 41control the synchrotron 12 and beam delivery apparatus 15 by usingtreatment information obtained by the above treatment plan. By virtue ofthis feature, regarding an irradiation position subjected to too muchirradiation dose by one-time ion beam irradiation, it is possible toperform a divided irradiation so as to reduce an irradiation dose foreach divided irradiation. This allows the difference in irradiation dosebetween the irradiation position subjected to the maximum dose and thatsubjected to the minimum dose to be reduced, thereby leveling offirradiation dose. In the example in FIG. 7, the maximum radiation doseis 10 at the spots in the layer 1, while the minimum radiation dose is6.3 at the spots in the layer 4. As a result, the capacity of thecapacitor of the position monitor 6B can be correspondingly reduced toenhance the resolution. This makes it possible to further correctlydetect an actual beam position during treatment.

(2) High-Accuracy Irradiation Effect by Preset Counter Clear

In this type of particle beam irradiation apparatus, in order to reducethe exposure of normal tissue to radiation to a minimum and perform aproper treatment with neither too much nor too little irradiation, thereis usually provided an irradiation dose monitor for measuring theirradiation dose of ion beam. When performing irradiation to each spot,a target irradiation dose is set on a spot-by-spot basis. Once theintegrated value of irradiation doses detected by the dose monitor hasreached the target value, a beam extraction stop command signal (beamstop command) is outputted to the accelerator, and in response to it,the accelerator stops the extraction of charged particle beam. Withtypical accelerator such as a slow cycling synchrotron or a cyclotron,even if the beam stop command is inputted, strictly speaking, it is notimpossible that some amount of response delay occurs rather than theoutput of the charged particle beam immediately stops.

In view of the above problem, in this embodiment, once the irradiationdose detected by the dose monitor 6A and counted by the preset counter41 a has reached a predetermined value, i.e., a target value (see step309), the preset counter control section 41A outputs a trigger signalfor triggering the scanning controller 41 to output the beam extractionstop signal to the high-frequency applying unit 9 (see step 312), and instep 311, clears the integrated count number of the preset counter 41 ato restart integration, without waiting for the actual stop of the beamfrom the accelerator.

FIG. 16 is a time chart showing the operations at this time. As shown inFIG. 16, a response delay can occur between the outputting of the beamextraction stop signal and the actual stoppage of the ion beamextraction from the synchrotron 12. During this response delay, theirradiation dose of ion beam extracted from the synchrotron 12 isintegrated after the aforementioned clearing. After the extraction ofion beam has been actually stopped, the irradiation position is changedto a next irradiation position (spot) by the processing in steps 209 and205 (see FIG. 12), and in step 302, the target count number is changed(in FIG. 16, for example, a change from the condition 1 (the targetirradiation dose to be applied to the spot situated at a position) tothe condition 2 (the target irradiation dose to be applied to the nextspot) is made). Here, the target count number is a count numbercorresponding to a target irradiation dose. In step 303, the scanningelectromagnets 5A and 5B are subjected to control, and in 305, theextraction of ion beam from the synchrotron 12 is restarted. At thistime, the irradiation dose at the aforementioned next spot after thebeam has moved there is detected by the dose monitor 6A and integratedby the preset counter 41 a, like the foregoing. The integration of countnumber then includes previously, as an initial value, the count numberwith respect to an immediately preceding spot during the time period ofthe response delay of the accelerator, and the irradiation dose at thespot subsequent to the aforementioned spot is added to this initialvalue (see the part “condition 2 setting” in FIG. 16). As a result,irradiating the above-described subsequent spot with ion beam extractedfrom the synchrotron 12 until a target irradiation dose is reached,means irradiating this spot with the irradiation dose obtained bysubtracting the aforementioned initial value from the target irradiationdose at this spot (i.e., the irradiation dose shown in “condition 2” inFIG. 16). Once the irradiation dose at this spot after the movement hasreached a target irradiation dose, the preset counter control section40A outputs a trigger signal for triggering the scanning controller 41to output the beam extraction stop signal to the high-frequency applyingunit 9, and clears the count number of the preset counter 41 a, like theforegoing. The irradiation dose during the time period of the responsedelay of the synchrotron 12 is added as an initial value in irradiatingthe spot after a further subsequent movement, and the same is repeatedhereinafter.

Because the scanning controller 41 performs the above-described control,when attempting to irradiate each spot, an ion beam is always applied tothe spot until the target dose of the spot is reached, on the assumptionthat an irradiation dose for the time period during a response delay ofthe synchrotron 12 occurring at irradiation to a spot is a part ofirradiation dose at a subsequent spot. If irradiation dose control isperformed without giving consideration to the response delay, anexcessive irradiation corresponding to response delay is performed. Thisraises the possibility that the irradiation dose becomes, e.g., 1.2 atall spots (the intended irradiation dose is represented by 1.0 as shownin FIG. 17). In contrast, in this embodiment, by performing theabove-described control, an ion beam dose (nearly equals 1.0)substantially equal to the target irradiation dose set with respect to apertinent spot can be applied to all spots except the first spot to beirradiated (i.e., the spot at the left end in FIG. 18) with highaccuracy, without an excessive irradiation corresponding to a responsedelay.

In this embodiment, based on the assumption that the irradiation dosecorresponding to a response delay of the synchrotron 12 occurring whenirradiating a pertinent spot is a part of the irradiation dose at a nextspot, an ion beam is applied to the pertinent spot until the target doseat the pertinent spot is reached. However, the same effect can beobtained using the following methods (1) and (2), as well.

(1) To output a trigger signal in step 310 based on the conditions that,in step 309 in the preset counter control section 41A, when, from thetarget irradiation dose at a spot, the irradiation dose corresponding tothe response delay occurring when irradiating immediately preceding spotis subtracted, and further when from the remaining irradiation dose, thecount number with respect to the spot during irradiation is subtracted,remaining irradiation dose has become zero, and that the set targetcount number has been inputted in step 302.

(2) To set the irradiation dose obtained by, from the target irradiationdose on a spot, subtracting the irradiation dose corresponding to theresponse delay occurring at the time of irradiating immediatelypreceding spot, as the target count number set in step 302 in the presetcounter control section 41A.

(3) Safety Enhancing Effect by Spot Timer

Since the dose monitor 6A is an machine, it is difficult to perfectlyeliminate the possibility that the irradiation dose monitor causes amalfunction or failure. Also, since the target irradiation dose for eachspot is usually a value transmitted from a data base or a valuecalculated based on the transmitted value, it is not impossible that animproper value is inputted at the stage of the transmission or thecalculation.

In light of the above, in this embodiment, the scanning controller 41has a spot timer, and determines whether an abnormal operation hasoccurred in accordance with the elapsed time after an ion beam startedto be extracted to one spot (see steps 306 and 307 in FIG. 14). If theelapsed time after the extraction start becomes no less than apredetermined time, the scanning controller 41 outputs an abnormalitysignal for indicating the occurrence of an abnormal operation (the firstabnormality signal) in step 308. Therefore, even if the extraction timeof the charged particle beam is likely to abnormally elongate due to amalfunction or an occurrence of failure of the dose monitor 6A, orimproper input value, the extraction of ion beam can be stopped after acertain time has elapsed. This reliably prevents excessive irradiationto an affected part, and further improves the safety.

(4) Safety Enhancing Effect by Maximum Dose Counter

Regarding the function of stopping the output of ion beam when theirradiation dose detected by the dose monitor reaches the target value,it is not impossible that equipment associated with this function causesa malfunction or failure. Also, it is not impossible that an erroroccurs in the setting of irradiation data.

In view of the above problems, in this embodiment, the maximum dosecounter control section 41C in the scanning controller 41 determineswhether any abnormal operation has occurred (see steps 322 and 323 inFIG. 14) in accordance with the magnitude relation between the countnumber detected by the dose monitor 6A and integrated by the maximumdose counter control section 41C and a predetermined regulated value. Ifthe count number becomes no less than a predetermined regulated value,the scanning controller 41 outputs a third abnormality signal in step324. Therefore, even if the ion beam does not readily to stop due to amalfunction or the like of the beam stopping function and theirradiation dose is likely to abnormally increase, the irradiation canbe stopped at a certain upper limit irradiation dose, thereby reliablypreventing an excessive irradiation to an affected part. This furtherenhances the safety.

Also, even if a target irradiation dose abnormally increases due to amalfunction or the like of data communications when an operator directlymanually makes a regulated value a set value using, e.g., a hard switch,and the charged particle beam does not readily stop due to a malfunctionor the like of the beam stopping function and the irradiation dose islikely to abnormally increase, the irradiation can be stopped at acertain upper limit irradiation dose, thereby reliably preventing anexcessive irradiation to an affected part. This further enhances thesafety.

(5) Deceleration Effect of Ion Beam Remained in Synchrotron atCompletion of Irradiation to All Spot in Layer

In the spot scanning irradiation according to the present invention, asthe size of a target changes, the number of spots in a layer changes,and consequently, the time required to complete an irradiation to allspots in the layer changes. Regarding the allowable extraction period ofsynchrotron, if it is set to be long with a large target assumed, theirradiation to all layers takes much time to complete, therebyelongating the treatment time for a patient. In view of the above, inthis embodiment, after the irradiation to all spots in a layer has beencompleted, the charged particle beam in the accelerator is decelerated,quickly outputs a remaining beam deceleration command, therebydecelerating ion beams in the synchrotron. This terminates the allowableextraction period of the synchrotron. As a result, the allowableextraction period is controlled to a requisite minimum, thereby makingthe treatment time with respect to a patient short.

The above-described ion beam irradiation by spot scanning can be appliedto a proton beam treatment system using a cyclotron serving as anaccelerator. This proton beam treatment system will be explained withreference to FIG. 19. The proton beam treatment system according to thisembodiment has a construction where, in the proton beam treatment systemshown in FIG. 19, the synchrotron is changed to a cyclotron 12A, and anenergy changing unit (a second element and a charged particle beamenergy changing unit) 42 is newly added. A charged particle beamgenerating unit 1A has a cyclotron 12A, which accelerates ion beams ofthe fixed energy. The cyclotron 12A has an acceleration unit 10A. Thecharged particle beam energy changing unit 42 is installed to a beamtransport system 4 in the vicinity of the cyclotron 12A. The energychanging unit 42 comprises a plurality of planar degraders (not shown)for passing ion beams therethrough to cause the ion beams to loseenergy, bending electromagnets (not shown) for deflecting the ion beams,which have been reduced in energy, and an aperture (not shown) forcutting out a part of the ion beams after passing the bendingelectromagnets. The energy changing unit 42 further includes a pluralityof energy adjusting plates having thicknesses different from each otherfor changing energy value. Ion beams are changed in energy value bypassing through the degraders. The plurality of degraders are madedifferent in thickness from each other in order to obtain a plurality ofenergy values.

As in the case of the embodiment shown in FIG. 1, the CPU 101 in thecentral control unit 100 reads the treatment planning information (seeFIG. 11) stored in the memory 103 from the storage unit 110, and causesthe memory (not shown) in the scanning controller 41 to store it. TheCPU 101 transmits to an accelerator controller 40A all of data ofoperational parameters concerning all layers out of the treatmentplanning information. Here, the data of operational parameters comprisesdegrader numbers and an exciting current value of each electromagnets inthe beam transport system, which are determined by the energy of ionbeams applied to each of the layers.

The control by the scanning controller 41 during the spot scanningaccording to this embodiment is performed similarly to the controlillustrated in FIGS. 12 and 14 in the embodiment shown in FIG. 1. Thecontrol by the accelerator controller 40A is the control by theaccelerator controller 40 shown in FIG. 12 except for step 214.Therefore, the accelerator controller 40A executes step 215 after step213. Here, out of the control by the accelerator controller 40A, thecontrol specific to this embodiment will be chiefly explained. In step202, the aforementioned data of operational parameters with respect toan i-th layer (e.g., the layer 1) is set. In step 203, the acceleratorcontroller 40A outputs degrader numbers to the energy changing unit 42,and outputs each exciting current value to a respective one ofelectromagnet power sources in the beam transport system 4.Specifically, the accelerator controller 40A performs control to inserta predetermined degrader in the energy changing unit 42 into beam path62 based on the degrader number, and based on each of the excitingcurrent values control, it perform to cause corresponding electromagnetpower sources to excite a respective one of electromagnets (firstelement) in the beam transport system 4. The entrance of ion beam intothe cyclotron 12A is performed by an ion source 11A.

The beam extraction start signal outputted from the scanning controller41 in step 300, and more specifically in step 305 (see FIG. 14), isinputted to the power source for the ion source 11A through theaccelerator controller 40A. Based on the beam extraction start signal,the scanning controller 41 activates the ion source 11A to apply ionbeams to the cyclotron 12A. When the beam extraction start signal passesthrough the inside of the accelerator control unit 40A, the acceleratorcontrol unit 40A outputs a predetermined high-frequency power set valueto the high-frequency power source (not shown) of the acceleration unit10A. Then, the ion beam in the cyclotron 12 is accelerated to thepredetermined energy and extracted from the cyclotron 12A through anextraction deflector 8. The energy of the ion beam is reduced to the setenergy by the degrader provided in the beam path 62, and reaches thebeam delivery apparatus 15 through the beam path 62. These ion beam isapplied to the pertinent spot in a pertinent layer in the target regionof a patient 30 by scanning of the scanning electromagnets 5A and 5B.

When the irradiation dose measured by the dose monitor 6A reaches atarget dose of the pertinent spot, the scanning controller 41 outputs abeam extraction stop signal in step 300, and specifically in step 312(see FIG. 14). The beam extraction stop signal is inputted to the powersource for the ion source 11A through the accelerator controller 40A.Based on the beam extraction stop signal, the scanning controller 41performs control to stop the ion source 11A and stop the application ofthe ion beam to the cyclotron 12A. When the beam extraction start signalpasses through the inside of the accelerator control unit 40A, theaccelerator control unit 40A controls the high-frequency power sourcefor the acceleration unit 10A to stop the application of ahigh-frequency power to the acceleration unit 10A. This terminates theirradiation of ion beam with respect to the pertinent spot. Hereinafter,the irradiation of ion beam with respect to a subsequent spot isperformed in the same manner as in the embodiment shown in FIG. 1.

According to this embodiment, the effects (1) to (4) produced in theembodiment shown in FIG. 1 can be achieved.

As is evident from the foregoing, according to the present invention,the detection accuracy with respect to an actual irradiation dose duringtreatment using charged particle beams can be enhanced.

Also, according to the present invention, the control accuracy withrespect to irradiation dose of charged particle beams can be improved.

Furthermore, according to the present invention, the excessiveirradiation of charged particle beams due to a monitor abnormality,input error, or the like can be reliably prevented.

Moreover, according to the present invention, the excessive irradiationof charged particle beams due to a malfunction of a beam stoppingfunction, or the like can be reliably prevented.

Besides, according to the present invention, the treatment time withrespect to a patient can be reduced.

1-40. (canceled)
 41. A treatment planning unit for creating a treatmentplan to perform the treatment with respect to an affected part, thetreatment planning unit comprising: an input unit; a computing unit thatsets a plurality of layer regions that are different in irradiationenergy from each other in the irradiation direction of a chargedparticle beam, in a target including an affected part set usingtomography image information including information on the affected part,that sets a plurality of irradiation positions of the charged particlebeam in each of these layer regions, that using an irradiation dose anda reference irradiation dose with respect to each irradiation positionset in each layer region, sets the number of times of irradiations ofthe charged particle beam with respect to each of the irradiationregions set in each of the layer regions, and that sets a plurality ofnumber of times of irradiations with respect to at least one saidirradiation position in the layer region to create a treatment planinformation with respect to the affected part; and a display unit fordisplaying the treatment planning information.
 42. The treatmentplanning unit according to claim 41, wherein the computing means setsthe number of times of irradiations with respect to one said irradiationposition so that the irradiation dose at said irradiation position foreach irradiation is no more than the reference irradiation dose. 43-54.(canceled)